1. Field of the Invention
The invention relates to a charging method of charging a holding body of an electrostatic image by a charging member arranged in a contactless manner and an image forming apparatus in which charging is executed by such a charging method.
2. Related Background Art
Among conventional image forming apparatuses, there is an image forming apparatus using a contactless charging system in which a charging roller as a charging member is arranged near the surface of a photosensitive drum as an image holding body and a voltage is applied between the charging roller and the photosensitive drum, thereby charging the surface of the photosensitive drum. According to the contactless charging system, the charging roller and the photosensitive drum have to be rotated at a same peripheral velocity while keeping a gap between the charging roller and the photosensitive drum to a small constant value.
FIG. 9 is a schematic diagram of a contactless charging apparatus disclosed in JP-A-2001-350321. According to such a charging apparatus, a gap between a charging roller 1 and a photosensitive drum 2 arranged in a contactless manner is formed by spacer members 3. That is, according to the charging roller 1, a resistive layer 1a is provided around the outer circumferential surface of a core 1b and the spacer members 3 are wound in the circumferential direction to both edge portions in the axial direction of the resistive layer 1a. The spacer member 3 is an adhesive sheet having a thickness of 20 to 200 μm made of polyester, polyethylene terephthalate, or the like in which one surface is formed on an adhesive surface. The spacer member 3 is wrapped while setting the adhesive surface to the inside.
Bearings 24 are attached to both edge portions of the core 1b of the charging roller 1. Springs 23 press the charging roller 1 onto the photosensitive drum 2 side through the bearings 24 by a predetermined pressing force. Thus, the spacer members 3 are come into contact with the surface of the photosensitive drum 2 and keep the gap between the charging roller 1 and the photosensitive drum 2 constant.
A photosensitive drum driving gear 22 to drive the photosensitive drum 2 is attached to one end of the photosensitive drum 2 and driven and rotated by a driving motor (not shown). A charging roller driving gear 21 to drive the charging roller 1 is fixed to one end of the core 1b of the charging roller 1 and driven and rotated by the photosensitive drum driving gear 22. Thus, the charging roller 1 and the photosensitive drum 2 obtain the rotation of the same peripheral velocity.
However, there is such a problem that in the case of rotating the charging roller 1 by the charging roller driving gear 21, the charging roller 1 is vibrated, so that the gap between the charging roller 1 and the photosensitive drum 2 is not stabilized and a charging spot occurs on the photosensitive drum 2.